Acoustic cavitation for agri-food applications: Mechanism of action, design of new systems, challenges and strategies for scale-up

Acoustic cavitation, an intriguing phenomenon resulting from the interaction of sound waves with a liquid medium, has emerged as a promising avenue in agri-food processing, offering opportunities to enhance established processes improving primary production of ingredients and further food processing. This comprehensive review provides an in-depth analysis of the mechanisms, design considerations, challenges and scale-up strategies associated with acoustic cavitation for agri-food applications. The paper starts by elucidating the fundamental principles of acoustic cavitation and its measurement, delving then into the diverse effects of different parameters associated with, the acoustic wave, mechanical design and operation of the ultrasonic system, along with those related to the food matrix. The technological advancements achieved in the design and set-up of ultrasonic reactors addressing limitations during scale up are also discussed. The design, engineering and mathematical modelling of ultrasonic equipment tailored for agri-food applications are explored, along with strategies to maximize cavitation intensity and efficiency in the application of brining, freezing, drying, emulsification, filtration and extraction. Advanced US equipment, such as multi-transducers (tubular resonator, FLOW:WAVE®) and larger processing surface areas through innovative designing (Barbell horn, CascatrodesTM), are one of the most promising strategies to ensure consistency of US operations at industrial scale. This review paper aims to provide valuable insights into harnessing acoustic cavitation's potential for up-scaling applications in food processing via critical examination of current research and advancements, while identifying future directions and opportunities for further research and innovation.

Plasma-activated liquids for mitigating biofilms on food and food contact surfaces

Plasma-activated liquids (PALs) are emerging and promising alternatives to traditional decontamination technologies and have evolved as a new technology for applications in food, agriculture, and medicine. Contamination caused by foodborne pathogens and their biofilms has posed challenges and concerns to the food industry in terms of safety and quality. The nature of the food and the food processing environment are major factors that contribute to the growth of various microorganisms, followed by the biofilm characteristics that ensure their survival in severe environmental conditions and against traditional chemical disinfectants. PALs show an efficient impact against microorganisms and their biofilms, with various reactive species (short- and long-lived ones), physiochemical properties, and plasma processing factors playing a crucial role in mitigating biofilms. Moreover, there is potential to improve and optimize disinfection strategies using a combination of PALs with other technologies for the inactivation of biofilms. The overarching aim of this study is to build a better understanding of the parameters that govern the liquid chemistry generated in a liquid exposed to plasma and how these translate into biological effects on biofilms. This review provides a current understanding of PALs-mediated mechanisms of action on biofilms; however, the precise inactivation mechanism is still not clear and is an important part of the research. Implementation of PALs in the food industry could help overcome the disinfection hurdles and can enhance biofilm inactivation efficacy. Future perspectives in this field to expand existing state of the art to seek breakthroughs for scale-up and implementation of PALs technology in the food industry are also discussed.

In-vitro evaluation of antimicrobial and insect repellent potential of supercritical-carbon dioxide (SCF-CO2) extracts of selected botanicals against stored product pests and foodborne pathogens

In the present study, the antimicrobial and the insect repellent activity of 16 botanical extracts obtained by supercritical CO₂ (SCF) extraction were evaluated. The present investigation was conducted as there is a necessity for exploration of natural botanical extracts that target both stored product insects and microbes. The antimicrobial activity was studied by disc diffusion and broth microdilution methods against ten microbial species, including Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis and Listeria monocytogenes), Gram-negative bacteria (Escherichia coli and Salmonella enterica), and fungi (Aspergillus flavus, Aspergillus paraciticus, Aspergillus ochraceous, Aspergillus niger and Penicillium verrucosum). Repellency assay was carried out by area preference method against three coleopteran insects (Tribolium castaneum, Rhyzopertha dominica and Sitophilus oryzae). Among all the extracts, thyme and ajwain were effective against all the tested bacteria with a minimum inhibition concentration (MIC) of 256-1024 µg/mL. Hop extract resulted in better antibacterial activity against all the tested Gram-positive bacteria with a MIC of 32-64 µg/mL. Oregano, thyme and ajwain extracts showed broad-spectrum antifungal activity against all the tested fungi with MIC of 128-1024 µg/mL. Most of the extracts exhibited class V (80.1-100%) repellency against T. castaneum. Extracts of hop, ajwain and thyme were found to have strong repellency against T. castaneum and R. dominica. Therefore, SCF extracts of ajwain and thyme can be explored further for the application of bio-extracts as a growth limiting factors in a microcosm where such consortia thrive.

Sono-photodynamic inactivation of Escherichia coli and Staphylococcus aureus in orange juice

Efficiency of blue (462 ± 3 nm) light emitting diode (LED) illumination to inactivate Escherichia coli and Staphylococcus aureus in the presence of exogenous photosensitizer (curcumin) was studied in freshly squeezed orange juice. Further, the combinational effect of ultrasound (US), photosensitizer (PS) and blue light (BL) on inactivation of microbes was evaluated. The effect of process parameters such as concentration of PS, US and volume of the juice on E. coli and S. aureus inactivation was also investigated. The US alone and PS + BL treatments resulted in 3.02 ± 0.52 and 1.06 ± 0.13 log reduction of E. coli; 0.18 ± 0.14 and 2.34 ± 0.13 log reduction of S. aureus, respectively. The combination of PS + US + BL treatment at optimized conditions resulted in 2.35 ± 0.16 log reduction of S. aureus. An additive effect on the inactivation of E. coli (4.26 ± 0.32 log reduction) was observed with PS + US + BL combination treatment. The US treatment showed significant change in cloud value, colour and browning index of orange juice. The combinational non-thermal processes (PS + BL and PS + US + BL) did not have any significant effect on total phenolic content, total flavonoid content, and hesperidin content of the orange juice. However, these processes affected ascorbic acid content and antioxidant activity negatively. Thus, this study indicated that photodynamic inactivation of E. coli and S. aureus using LED-based photosensitization in fruit juices could be a potential method for microbial inactivation. Nevertheless, the effect on quality parameters needs to be considered while optimizing the process.

Development and validation of headspace Solid-Phase microextraction coupled with gas chromatography (HS-SPME-GC) method for the analysis of zingiber zerumbet L

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography (GC-FID) was explored to determine the fingerprinting characteristic of Zingiber zerumbet L. volatiles to differentiate between different ginger species. The effect of different fibers [polydimethylsiloxane (PDMS, 7 μm), polyacrylate (PA, 85 μm)], different temperature and time on the HS-SPME-GC was investigated by using response surface methodology coupled with full factorial experimental design. The area percentage of the major sesquiterpenes (Zerumbone and α-humulene) were 56.3 ± 4.7% and 47.5 ± 27.2% with PA fiber, respectively at optimum condition of 70 °C and 30 min. Validation of the developed HS-SPME-GC method with limits of detection and quantification for zerumbone was 0.09 and 0.28 μg/g, respectively, demonstrating the suitable sensitivity of HS-SPME-GC method for the quantification of sesquiterpenes. Therefore, the simplicity of HS-SPME-GC makes it a convenient tool for qualitative and quantitative comparison of different ginger species targeting at the marker sesquiterpene molecule, zerumbone.

Efficacy of blue LED in microbial inactivation: Effect of photosensitization and process parameters

Efficacy of blue (462 ± 3 nm) Light emitting diode (LED) illumination to inactivate the foodborne pathogens like Escherichia coli and Staphylococcus aureus in the presence of exogenous photosensitizer (curcumin) was studied in vitro. The effect of temperature, concentration of photosensitizer and incubation time with photosensitizer for microbial inactivation was investigated and sublethal injury of cells was determined. Mechanism of inactivation by the combination of photosensitizer and blue light was also examined. A maximum reduction of 5.94 ± 0.22 and 5.91 ± 0.20 log CFU/ml was obtained for E. coli and S. aureus, respectively, when treated with photosensitizer (20 μM) at 13 J/cm² of blue light. There was no significant change in the inactivation of these pathogens both at 9 °C and 27 °C in the presence of photosensitizer. Even, the incubation with the photosensitizer didn't show any significant difference on the inactivation of these food-borne pathogens. Sublethal injury (>90% injury) was also observed for the cells treated with photosensitizer and blue light simultaneously. Confocal laser scanning microscopy analysis revealed that membrane integrity was disturbed due to photodynamic activity of curcumin in both the bacteria. Further, both cells produced intracellular reactive oxygen species by the action of photosensitizer and blue light. Scanning electron microscopy of E. coli and S. aureus cells treated with photosensitizer and blue light showed morphological changes in the cell wall compared to untreated group. The study indicated that photodynamic inactivation of foodborne pathogens using LED-based photosensitization can be explored as a potential technique for food safety.